3 Interstellar analysis

Inspection of the $\it FUSE$ absorption spectra shown in Figs. 1 and 2 reveal significant detections of the important interstellar absorption line of O VI (1031.9 Å), as well as detections of the ground state resonance lines of interstellar O I (1039.2 Å), C I (1139.8 Å), Ar I (1048.2 Å), N I (1134.9 Å), Fe II (1143.23 $\&$ 1144.9 Å) and P II (1152.8 Å). It is immediately apparent from these line profiles that many of the strongest absorption lines are accompanied by a well resolved high-velocity (HV) component at $V_{\rm LSR}$ $\sim$ +65 kms^-1. We identify this as the high velocity component observed by WJ in both the Na I and Ca II interstellar lines at $V_{\rm LSR}$ = +69 kms^-1 towards HD 47240.

Unfortunately we do not uniquely detect the $V_{\rm LSR} = -31$ kms^-1 component (that was seen in the visible Na I lines towards HD 47359 by WJ and in Ca II towards HD 47240 by Sfeir 1999) in our present $\it FUSE$ spectra. This is presumably due to blending of this component with the strong central line-of-sight absorption at $V_{\rm LSR}$ = +3 kms^-1that is not resolved by the $\it FUSE$ instrument. However, we note that the asymmetry in the blue-wing of the weak Fe II 1143.23 Å line is most probably due to an absorption component at $\sim$- 30 kms^-1. Additionally, we also detect many of the lines associated with the Lyman (B-X) and Werner (C-X) bands of the H₂ molecule in these $\it FUSE$ spectra (some of which are also accompanied by an HV component at +65 kms^-1) whose detailed analysis will be deferred to a future paper.

For each of the atomic lines that are accompanied by a detection of the HV component we have fitted their local stellar continua with a multi-order polynomial to produce a residual intensity profile. The placement and shape of a stellar continuum was guided by those of the many stellar absorption lines observed throughout the $\it FUSE$ spectrum. The interstellar absorption profiles were then fit with one or more absorption components (i.e. "clouds'') using line oscillator strengths listed by Morton (2001). This fitting procedure is discussed in detail by Sfeir et al. (1999), such that each theoretical absorption profile is described by a gaussian velocity dispersion parameter, $\it b$, a cloud component LSR velocity, V, and a cloud column density, N. These best-fit values of V, $\it b$ and N for all the detected interstellar lines are also listed (together with their respective errors and equivalent width values) in Table 1.

 

 

Table 1: FUSE spectra - HD 47240 absorption line measurements.

Line	$W_{\lambda }$	$V_{\rm LSR}$	b	N	S/N
	(mÅ)	(kms-1)		(1012 at cm-2)
C I 1139.....	28.2	61.2 (0.6)	9.6 (0.9)	182 (34)	19
N I 1134.4.....	43.2	71.8 (0.4)	9.4 (0.6)	175 (31)	16
N I 1135........	49.4	73.1 (0.4)	10.4 (0.6)	137 (18)	16
O I 1039........	47.5	68.4 (2.3)	11.7 (3.1)	724 (42)	15
O VI 1032.....	74.9	2.3 (0.8)	17.3 (1.1)	82 (14)	11
(u)	<9	HV		<7
P II 1153......	8.8	63.9 (1.1)	7.9 (1.7)	4 (1)	20
Ar I 1048.....	20.9	66.4 (0.6)	8.5 (1)	9 (2)	16
Fe II 1143.....	10.9	65.4 (1.4)	9.5 (2.1)	55 (12)	17
Fe II 1145.....	53.5	66.6 (0.5)	14 (0.7)	58 (7)	16
(u)- Upper limits on the HV component.

In Fig. 3 we show the FUV residual intensity profiles that possess an HV feature together with their respective best-fit profile models.

Figure 3: FUSE spectra absorption profile fitting for HD 47240; results are given in residual intensity. Solid bars indicate typical error sizes to the continuum level fits.

Note that since the strong, central components of these line profiles (which occur at $V_{\rm LSR}\sim 3$ kms^-1) are all saturated and their best-fit column densities are thus highly uncertain, we present only the fit data to the well resolved, weaker high velocity component for each line species.

 

 

Table 2: IUE spectra - HD 47240 absorption line measurements.

Line	$W_{\lambda }$	$V_{\rm LSR}$	b	N	S/N
	(mÅ)	(kms-1)		(1012 at cm-2)
C II* 1336......	70	59.2 (0.9)	12.1 (1.8)	171 (25)	28
C IV 1548(u).......	<15	HV		<3
O I 1302........	80	66.1 (0.8)	11.6 (1.9)	>350(s)	20
Mg II 3p 2796/2803	460/386	57.7 (1.5)	11.9 (2.7)	>110(s)	17
Mg I 2852........	107	66.7 (2)	5.7 (6)	1.6 (5)	14
Al II 1670.......	80	67.0 (0.8)	12.1 (1.7)	4.2 (1)	32
Al III 1855(u).....	<12	HV		<50
Si II 1304.....	99	66.1 (1.2)	13 (2.4)	150 (14)	18
Si IV 1394(u).......	<24	HV		<3	19
S II 1253....	37	65.2 (1.7)	9.9 (2.3)	290 (90)	23
Fe II 1608........	65	72 (0.9)	8.3 (2.3)	70 (43)	20
(u)- Upper limits on the HV component.
(s)- Saturated lines.

In Figs. 4 and  5 we also show the high resolution absorption profiles of the Na I and Ca II lines towards HD 47240 (from Sfeir 1999) and in Fig. 6 we show the near ultraviolet absorption profiles of the Al II (1670 Å), Si II (1304 Å), S II (1253 Å), Fe II (1608 Å), C II* (1336 Å), Mg I (2852 Å) and Mg II (2800 Å doublet) lines as recorded by $\it IUE$.

Figure 4: Na I absorption profile fitting for HD 47240. Data taken from Sfeir (1999).

Figure 5: Ca II absorption profile fitting for HD 47240. Data taken from Sfeir (1999).

Figure 6: IUE absorption profile fitting for HD 47240; results are given in residual intensity. Solid bars indicate typical error sizes to the continuum level fits.

We note that the positive high velocity component seen in the $\it FUSE$ data is also detected at a very similar velocity in many of the profiles of the strongest absorption lines recorded by the $\it IUE$ satellite and also in the ground based data. The best fit values for V, $\it b$ and N for the (partially resolved) HV components of these lines are listed in Tables 2 and 3, and their derivations have been discussed in detail in Sfeir (1999). We note that the column density values derived from both the $\it IUE$ and $\it FUSE$ spectral lines for N(Fe II) are (within the errors) in general agreement. Since the $\it FUSE$ derivation was obtained using a constrained fit to the Fe II doublet at 1144 Å we believe this to be a more accurate determination of column density and thus we use N(Fe II) = 13.75 $\pm$ 0.08 cm^-2 in all future calculations. For the case of N(OI), we use the valued derived from the FUV line of 1039.2 Å since the OI 1302 Å line is saturated. Unfortunately the HV components detected in both of the Mg II lines are saturated and in Table 2 we list a minimum value for N(MgII) which will not be used in the subsequent analysis of element abundances in Sect. 5 due to its inherently large error estimate.

Our high resolution ground-based observations of the Ca II line towards HD 47240 indicate that this HV component is actually a blend of (at least) two absorbing clouds at $V_{\rm LSR}$ $\sim$ +60 and $V_{\rm LSR}$ $\sim$ + 71 kms^-1. However, the lower resolution $\it FUSE$ and $\it IUE$ observations were unable to resolve these two clouds and it was found that the best fit to the HV component in all the UV data was obtained using a one-cloud absorption model centered at $V_{\rm LSR}\sim + 65$ kms^-1.

 

 

Table 3: Na I (D2/D1) and Ca II doublet absorption line measurements for HD 47240.

Line	$W_{\lambda }$(D2)	$W_{\lambda }$(D1)	S/N	$V_{\rm LSR}$	b	N
	(mÅ)	(mÅ)		(kms-1)		(1011 at cm-2)
Na I........	601.6	475.9	150	-16 (0.1)	5.6 (0.1)	8.8 (0.0)
				2.4 (0)	2.5 (0.1)	3934 (1256)
				12.1 (0.1)	4.4 (0.1)	15.2 (0.6)
				59.6 (1.4)	1.1 (3.9)	0.5 (6.6)
				70.6 (0)	1.9 (0.1)	10.9 (1.1)
Line	$W_{\lambda }$(K)	$W_{\lambda }$(H)	S/N	$V_{\rm LSR}$	b	N
	(mÅ)	(mÅ)		(kms-1)		(1011 at cm-2)
Ca II........	356.2	224.7	120	-37.1 (a) (1.4)	1.6 (2.4)	0.5 (1.3)
				-16.4 (0.1)	9.2 (0.2)	13.5 (0.1)
				7.6 (0)	7.3 (0)	50.1 (0.1)
				62 (0.3)	1.9 (0.7)	1.7 (1.3)
				74 (0.1)	2.1 (0.3)	8.3 (2.8)
(a)- The line is not present in Na I, but faint in Ca II.